TECHNICAL FIELD
This invention pertains to remotely controlled unmanned drones.
Remotely controlled airborne unmanned drones are used for many purposes, including the testing and evaluation of weapons systems by various armed services. In particular, the military has found target drone formation flying to be significant in the evaluation of weapon systems. Certain control drone formation flying arrangements presently available utilize ground station computer control to maintain each aircraft's position in four dimensional space (XYZT). In the simplest example, with two airplanes flying in drone formation, the ground station would multilaterate or use triangulation to determine the position of each individual aircraft. The ground station independently triangulates the position of each aircraft. The disadvantage of this approach is that it takes a significant development to provide software in the ground stations for every new aircraft type that is to be adapted to this system. Accordingly, a system of this type is very expensive to develop and maintain. Perhaps more significantly, systems of this type are most appropriate for controlling complex drone formations flying on a grid system based range. A further disadvantage of this prior arrangement is it is not effective when flying the drone formation outside the range of triangulation stations that is necessary for the prior arrangement. This presents a clear disadvantage for flying drone formations over the oceans. It is even more difficult where the drone formations are over the horizon from the ground control stations.
In an attempt to avoid some problems, it is common to utilize "high flyer" aircraft as control stations. Or alternatively, to utilize shipboard platforms. Adding even additional complexity is the utilization of both high flying aircraft and shipboard stations for providing formation control.
A drone range tracking system is the means by which drones are tracked while traversing a range. It provides positional information to a drone controller. Two types of drone range tracking systems are currently in use; grid range and rho-theta. In grid range system, the range is grid mapped. Ground relay stations are placed at surveyed points on the grid. Then drone command/telemetry time of arrival and trilaterization are used to fix a drone's position in x, y, z coordinates.
A rho-theta system consists of a tracking radar that returns range (rho), azimuth (theta), and elevation from the surveyed radar station to the drone. The majority of drone ranges are solely dependent upon rho-theta tracking systems for positional data. Rho-theta systems cannot provide the accuracy to control multiple drones in close formation, since rho-theta errors are typically 190 ft. RMS in range and, at distances of 100 nautical miles, 600 ft. RMS in azimuth and 1,200 ft. RMS in elevation.
Several command/telemetry systems are used at the different ranges. These systems dictate the form and characteristics of the uplink commands for controlling the airborne drones and the downlink telemetry of drone parameters for ground station monitoring.
In a proposed next generation arrangement which is to permit flight of drones in formation and, in particular, is also directed toward providing over-the-horizon control capability, each drone will have a global positioning system (GPS) receiver. The GPS position from each drone is downlinked to a ground station or to a high flying aircraft. The GPS position is received and is used to control the flight of the drones to prevent collision. A disadvantage again of this type of arrangement is that the ground station will require a significant amount of software along with the expense of developing such software. The one advantage of the GPS approach is that no longer will it be required to multilaterate.
It is desirable to provide a drone formation control system which would be more independent of ground stations, and be independent of command/telemetry system types and aircraft types. It is further desirable to provide an automatic drone formation control system which is independent of the particular drone range.